THE doona isn't quite dancing, yet, but the inclusion of two frisky intruders has seen sexual activity in the Big Brother house and PG-program explode.

A steamy spa session between new housemate Ava and resident ladies' man Josh aired on Monday night's show and ended with the pair sleeping together - but not in the biblical sense, producers assert.

As the series hits the 40 days and 40 nights mark, the instant and intense couple were involved in a "pashing and light petting session," which threatens to test the boundaries of the revamped kid-friendly format.

The pair became physical during an evening pool party involving the group, but separated from the pack - and Josh's ardent admirer Angie - to share their first steamy kiss.

The show's executive producer, Alex Mavroidakis, denied any adults-only content would go to air but admitted that "when two people want to get it on, it's going to happen".

"We have got a format to protect, but we're not going to stop them from doing whatever they want. It's not that we're trying to sweep it under the carpet, we just can't show it if they did."

He said it would be Channel 9's decision to commission a naughtier, up-late version of the show, but the network has been steadfast in staying away from raunchier content this year.

The addition of a new "alpha male" Sam should further shake up relationships in the house, with the 21-year-old Gold Coast bartender making it clear he was open to female persuasion.

"I'm the type of guy whose always open to offers and won't say no if something were to arise."

After an initial meeting with country boy, Bradley, he will be introduced to the BB women first during a speed-dating dinner party where it is understood he connects with Layla and Estelle.

The latter's emotional meltdown following her third eviction nomination raised concerns she was not coping in the social experiment.

But Mavroidakis and the show's psychologist Dr Sarah Angel said the brash legal student was more resilient than she looks.

This week, producers called Estelle to the Diary Room to check on her welfare after her weekend breakdown, as her friendship with Ava seemed to further isolate her from the other female housemates.

But Dr Angel said her teary responses have been part "reaction" to nominations and "release" from the pressure and anxiety of the process.

"They are all self-sufficient and no one has been showing any signs of vulnerability or distress that I should be worried about. Estelle is very resilient and actually really good at managing her emotions."